A major obstacle for hydroelectric projects is opposition from environmental groups.
Projects encountering this problem include China's Three Gorges project on the Yangtze River, Hydro-Quebec's Great Whale River project in Canada, Mexico's Rio Usumacinta dam, Chile's Pangue Project on the Bo-Bo River, Malaysia's Bakun project, India's Narmada River project, and Nepal's Arun project.
Finance is another problem.
Often, environmental opposition makes the World Bank reluctant to fund projects.
High costs have delayed China's Three Gorges project, Kenya's Ewaso Ngiro project, Argentina's and Paraguay's Yacyreta dam, Nepal's Arun project, Turkey's south-east Anatolian project, and Iran's planned Karun River projects.
Projects encounter opposition over the displacement of people or the destruction of cultural and historic resources.
China's Three Gorges project would displace many people in Sichuan Province.
Mexico postponed its Rio Usumacinta dam partly because of the possibility of flooding Mayan cities.
Canada's Great Whale River project is opposed by the province's aboriginal community.
Malaysia's Bakun project poses many technical and ecological challenges, as well as the possibility of damaging a unique tribal culture.
Political issues plague many projects.
The Yacyreta dam was delayed by Argentina's numerous political and economic crises.
Malaysia's Pergau project is opposed by the state government of Kelantan.
Hungary considers Slovakia's attempt to divert the River Danube to its own Cunovo project a territorial violation.
Turkey's south-east Anatolian project poses political problems with Syria and Iraq.
Projects which haven't encountered such difficulties include Portugal's Vila Nova de Foz Coa dam, China's Xiaolangdi project, and Paraguay's Corpus Cristi dam.
